1. Field of the Invention
The present invention relates to an image processing method, and more particularly, to a method for defining chromaticity regions according to luminance levels and adjusting the chromaticity of images accordingly.
2. Description of the Prior Art
A skin-tone correction method is designed to adjust chromaticity of a pixel by first determining whether a chromaticity vector of the pixel is within a predetermined skin-tone region, i.e. first determining whether a video of the pixel looks like human skin, and then rotating the chromaticity vector of the pixel toward a central axis in the predetermined skin-tone region by a predetermined adjusting angle. After determining that the chromaticity vector of the pixel is indeed within the predetermined skin-tone region, the video of the pixel, with an adjusted chromaticity vector, looks more like human skin.
However, a color model where the chromaticity vector is located looks like an olive, with a wide waist and a narrow head and tail. A first position where a first pixel is located in the color model is different from a second position where a second pixel has a luminance level different from that of the first pixel, even though the first pixel has a chromaticity vector totally the same as that of the second pixel. In other words the first pixel, assumed to have too large a luminance level to fall in a region inside of the color model and probably not having its first chromaticity vector within the predetermined skin-tone region, is likely to be determined the same as the second pixel, which has a second chromaticity vector the same as the first chromaticity vector, but a smaller luminance level and is located within the olive-shaped color model. Therefore, the skin-tone correction method is likely to erroneously determine a nonhuman pixel, which is located in a region outside of the olive-shaped color model, to be a human pixel.
Moreover, the predetermined skin-tone region is very small, so the skin-tone correction method is likely to erroneously determine a human pixel to be a nonhuman pixel.
Lastly, after determining that the pixel is indeed human skin, the skin-tone correction method rotates the chromaticity vector toward a central axis by a constant adjusting angle, which lacks flexibility, and can be inaccurate.